The present invention generally relates to a linear driving apparatus using two units of linear motors with the rotors being coupled to each other, and more particularly, to a linear driving apparatus for controlling the operation of the position and the speed at a high accuracy.
FIG. 11 is a plan view illustrating the appearance of a linear driving apparatus having been designed previously by the inventors, while FIG. 12 is an electric block diagram of the linear driving apparatus. In the previous design of FIGS. 11 and 12, there are provided two units of linear motors 10 and 20, which are three-phase brushless linear motors. By the independent speed controlling operation of the linear motors 10 and 20, the stators 11 and 22 coupled by a coupling member 30 which may move freely, with the gap being open, with respect to the stators 11, 21 are basically to be driven in a driving direction as shown in the drawing. In further detail, photo detectors 124 and 125 corresponding to linear scales 113 and 114 pasted on the sides of the stators are provided respectively on the sides of the coupled rotors 12 and 22. The signals transmitted from the photo detectors 124 and 125 as the positional information of the rotors 11 and 12 are introduced into a linear motor portion 40 which mainly includes micro-computers. The impellent force to be caused by the rotors 12 and 22 are adjusted independently by the linear motor control portion 40 so that a moving object (not shown) secured on the rotors and 22 may move at a predetermined speed. Polyphase windings 121 and 221 are secured on the reverse faces of the rotors 12 and 22, and hall elements 123 and 223 for detecting the magnetic poles of the magnetic flux to be transmitted from the stators 11 and 21 are secured thereon so as to give the timings from the polyphase excitation in the polyphase windings 121 and 221 to the linear motor control portion 40.
However, in the above-described conventional embodiment, as the linear motor 10 and the linear motor 20 are adapted to effect independent controlling operations, the linear motor controlling portion 40 is inevitably required to be made more complicated by including a considerable number of components such as photo detectors 124, hall elements 123, etc. which are required. Thereby, large obstacles are caused in lowering the cost of the apparatus. Some differences in the impellent force to be caused in the linear motors 10 and 20 may cause the moving object to be yawed. Particularly, when controlling the operations of the position and the speed at higher accuracy, some differences in the impellent force become large disturbance factors in the control system.